This paper describes a methodology for predicting outflow from a rupture in a pipeline transporting supercritical ethylene. Ethylene outflow is of particular interest and is a challenging scenario to model as typical operating temperatures are a few degrees above the critical temperature, 283 K. Thus when the pipe fractures the initial rapid depressurisation induces a number of propagation waves to travel up the pipeline initiating phase changes and fundamentally changing the nature of the outflow problem. The methodology presented is primarily based on an outflow model for compressed volatile liquid outflow as this is demonstrated to be the flow regime upstream of the pipe fracture after a small time interval following pipe fracture. The model is validated using a more complex commercially available pipeline model, PROFES for propane outflow as experimental data at relatively low pressure and short pipes exist in the open literature and has been used to validate the models considered here. Finally the ethylene outflow methodology has been applied to a number of different ethylene pipeline scenarios with a range of operating temperatures, pressures and pipeline diameters of interest to confirm that predicted outflow rates trend as expected. (C) 2006 Elsevier Ltd. All rights reserved.